Patent Cooperation Treaty (“PCT”) International patent application PCT/2003/024255 entitled “Sealed Integral MEMS Switch,” published 12 Feb. 2004, with International Publication Number WO 2004/103898 A2 (“the PCT patent application”), discloses an integral MEMS switch which couples an electrical signal present on a first input conductor either to:
1. a single output conductor; or
2. to either a first or a second output conductor.
The MEMS switch disclosed in the PCT patent application includes a micro-machined monolithic layer of material having:
                a. a seesaw;        b. a pair of torsion bars that are disposed on opposite sides of and coupled to the seesaw, and which establish an axis about which the seesaw is rotatable; and        c. a frame to which ends of the torsion bars furthest from the seesaw are coupled.The frame supports the seesaw through the torsion bars for rotation about the axis established by the torsion bars. The seesaw carries either one or two electrically conductive shorting bars that are located away from the rotation axis established by the torsion bars at either one or both opposite ends of the seesaw.        
The MEMS switch also includes a base that is joined to a first surface of the monolithic layer. A substrate, also included in the MEMS switch, is bonded to a second surface of the monolithic layer that is located away from the first surface thereof to which the base is joined. Formed on the substrate are either one or two electrodes which are juxtaposed respectively with a surface of the seesaw that is located to one side of the rotation axis established by the torsion bars. Applying an electrical potential between one electrode and the seesaw urges the seesaw to rotate about the rotation axis established by the torsion bars thereby narrowing a gap existing between the electrode and the seesaw.
Also formed on the substrate are either one or two pairs of switch contacts each of which connect to the input conductor and to the output conductor or respectively to the two output conductors. The pair or pairs of switch contacts:                a. are disposed adjacent to but spaced apart from the shorting bar(s) when no force is applied to the seesaw;        b. are electrically insulated from each other when no force is applied to the seesaw; and        c. upon application of a sufficiently strong force to the seesaw which urges the seesaw to rotate are contacted by a shorting bar.In this way, contact between the shorting bar and a pair of switch contacts electrically couples together the input conductor with an output conductor.        
Another aspect of the PCT patent application is a MEMS electrical contact structure and a MEMS structure which includes a first and a second layer each of which respectively carries an electrical conductor. The second layer also includes a cantilever which supports an electrical contact island at a free end of the cantilever. The electrical contact island has an end which is distal from the cantilever, and which carries a portion of the electrical conductor that is disposed on the second layer. In this particular aspect of the PCT patent application the portion of the electrical conductor at the end of the electrical contact island is urged by force supplied by the cantilever into intimate contact with the electrical conductor that is disposed on the first layer. In the MEMS switch, this cantilever structure provides an electrical connection to ground plate(s) which are disposed adjacent to and are electrically insulated from the MEMS switches input and output electrical conductors.
Disclosure
An object of the present disclosure is to provide an improved MEMS switch.
Another object is to provide a hermetically sealed MEMS switch using a novel combination of anodic bonding and glass frit.
Yet another object of the present invention is to provide a MEMS switch, including single-pole single-throw, or single-pole multiple-throw, or multiple-throw multiple-pole switches, that is adapted for switching radio frequency (“RF”) alternating currents.
Another object of the present invention is to provide a smaller MEMS switch.
Briefly, a single-pole, double-throw (“SPDT”) micro-electro mechanical systems (“MEMS”) switch that selectively couples an electrical signal present on an input conductor connected to the SPDT MEMS switch to a first or a second output conductor also connected thereto, or conversely.                1. A SPDT MEMS switch includes a micro-machined monolithic layer of material having at least a pair of actutatable toggles. The pair of toggles may be configured in any desired orientation. In the preferred implementation, torsion bars support the actuating toggle from a surrounding frame. The torsion bars are on opposite sides of the toggle and establish an axis about which the toggle can rotate. Each of the toggles carries an electrically conductive shorting bar at an end thereof which is furthest from the toggle's rotation axis. Each toggle thus represents an individual single-pole single-throw (SPST) switch.        2. Another objective of the invention is to allow the construction of arbitrary arrangements of SPST toggle switches to form more complex switch networks. Many individual toggles can be created within the sealed cavity, and judicious design and layout allows the creation of a monolithic network of switches within the sealed cavity. In general, given a plurality of toggles connected in a judiciously chosen fashion, it is possible to create single-pole single-throw switches, single-pole multiple-throw switches or multiple-pole multiple-throw switches. Since each toggle element can function independently of each other toggle element it is also possible to have more than one toggle closed at the same time. Because the individual switches are very low loss, viable switch networks can be constructed with an arbitrary input connected to an arbitrary output via several switches. It is also possible to have multiple individual switch configurations within the same package; for instance, a single monolithic component can contain a SPDT MEMS switch (1×2) along with a SP4T switch (1×4). In the disclosed implementation each toggle functions independently and it is possible to close as many or as few switches as desired at any time, allowing for example a single input to be connected to multiple outputs simultaneously.        
Another aspect of the present invention is a method for anodic bonding which forms a strong bond using glass frit as a gasket to hermetically seal metal feedthroughs. Included in this invention is a method of increasing the surface contact area to the sealing glass using a rail or other feature formed on the bond surface that is not initially patterned with the sealing glass. This rail or other feature will push into the sealing glass during the bonding process. It will be readily apparent to those of skilled in the art that this sealing technique can be used for various MEMS and other mechanical and electrical devices which require wafer level hermetic sealing.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.